1. Field of the Invention
This invention relates to a method and apparatus for rating in numerical values the luster of the surface of a painted plate, an anodic oxidation film-carrying aluminum plate and lacquer ware.
2. Description of the Prior Art
It is considered that the luster of a surface can be rated by degrees, which are determined by the human eye, of the gloss, clarity, or distinctness or sharpness of image as it is sometimes called, and lightness, the three optical factors, of the surface. Devices for determining and displaying the degrees of these three optical factors independently have been developed, but a method of and a device for synthesizing the three factors of the luster of the surface of an object to rate the luster thereof are not available.
The gloss is related to the intensity of the specularly reflected light, which is determined as mirror surface gloss, or specular gloss, by a conventional gloss meter. However, mirror surface gloss does not correspond exactly with visual gloss.
The clarity of the surface of an object is rated in accordance with the image reflecting capability thereof, i.e. the degree of distortion of an image reflected therein. There is a conventional method of optically determining the image reflecting capability of a surface, JISH 8686 "Test Method for the Image Clarity of Anodic Oxidation Coatings of Aluminum and Aluminum Alloy", but this is a method of determining only the image reflecting capability of a surface.
In case of, for example, an anodic oxidation film, an extremely thin, nearly semitransparent outer layer exists on the outer surface thereof. The outer surface as a whole of this film looks misty even when it has high degrees of gloss and visibility. Thus, the brightness, which is an optical factor other than the gloss and visibility, of a surface has an influence upon the luster thereof.
As described above, these three optical factors have different characteristics. However, when the surface of an object is observed with the naked eye, the degrees of the three optical factors thereof are sensed simultaneously and determined collectively as the luster thereof. A method of visually determining the luster of a surface has not yet become available. Therefore, there has been no choice, up to now, but to determine and display the degrees of the three optical factors of a surface separately.
A method of displaying the luster of a surface rationally so that the luster value displayed agrees with that determined visually has not yet become available. A general-use apparatus for visually determining the luster of the surface of an object and the problems of such apparatus will now be described. FIG. 1 is a diagram of the construction of a conventional apparatus of this kind. The figure of a test pattern 2 illuminated directly by two lamps 1 is reflected twice on two mirrors 3 and is then projected onto a sample 4. The figure of the test pattern 2 is shown in FIG. 2. The figure consists of arbitrary numerals of 13 sizes graduated as 0.1, 0.2, . . . 1.0, 1.2, 1.5, 2.0. When this test pattern is projected on the sample 4, the image of the figure varies depending upon the condition of the surface of the sample. If the surface on which the test pattern is projected is a perfect mirror surface, even the smallest numeral in the projected image is reflected clearly without any shaded portions and distorted lines. Even a coated surface and an evaporated surface which are finished by highly-advanced techniques usually have minute projections and recesses and gently-waved portions, which cause the projected image to be distorted. In order to determine by this apparatus the degree of luster of a coated surface of an industrial product, for example, an automobile, a standard degree of smoothness of a finished surface is set, and a numerical value corresponding to this standard degree of smoothness is determined as a Gd value. The luster of a coated surface is judged in accordance with this Gd value, as to whether it meets the standard or not.
A method of determining the degree of luster of a coated surface will now be described. The image projected on the sample 4 in FIG. 1 is reflected twice on two mirrors 5. A graduation (Gd value) corresponding to a numeral which can be read through an ocular cylinder 6 is read. The results of judgements of degree of luster made by this conventional apparatus have a low reproducibility and a low accuracy, and differ greatly depending upon the persons who operate the apparatus.
The inventor of the present invention, before developing a luster rating method, considered the causes of the drawbacks encountered in the above conventional method and apparatus, taking into consideration the importance of the gloss and clarity (image reflecting capability) of a surface, which constitute the luster thereof.
The first cause resides in the fact that the test pattern consists of numerals which are not regularly-shaped but irregularlyshaped. Therefore, some numerals can be read and some can not, even when all of these numerals have the same size and represent the same graduation of luster. In some cases, a numeral is read favourably by mistake as some other similarly-shaped numeral. For example, the numbers 8, 9 and 3, the numbers 7, 4 and 1, and the numbers 3 and 5 have somewhat similar shapes, so that they are apt to be mistaken for one another. Since a numeral consists of straight and curved lines of various thicknesses and lengths, the visual power of an examiner has a great influence upon the results of a luster determining operation. This constitutes a cause of the occurrence of great differences among the judgements made by different persons of the luster of a surface.
The second cause resides in the fact that the surface of a sample has directional properties. For example, a plate of Alumite containing aluminum as a base has some orientation of its surface due to the rolling step to which the plate was subjected during manufacture, and a coated plate also has some orientation due to the coating step to which it was subjected during manufacture. Thus, the surfaces of materials generally have orientation in the longitudinal and lateral directions thereof. A test pattern consisting of numerals is composed of a combination of lines which extend in an extremely complicated manner in the longitudinal and lateral directions, such as inclined lines, curved lines and waved lines. Therefore, when test patterns of this type are projected on mirrors to examine the reflecting capability of the surfaces of the patterns, different results are obtained due to the different directional properties of the finished surfaces even if the surfaces look identical.
The third cause resides in the system for illuminating a pattern directly by two lamps as shown in FIG. 1. Due to this illuminating system, the direct light from the lamps is mixed in the projecting light, so that it is often difficult to judge the degree of luster of a surface having a high degree of gloss.
The fourth cause resides in the use of four mirrors. Let the image reflecting capability of a perfect mirror surface be 100%. The actual image reflecting capability of the mirrors used in this type apparatus, since they are obviously not perfect, is not more than 90%. When four such mirrors are used, the drawbacks thereof are necessarily cumulative. Consequently, the grade of clarity given to a sample is lower than the actual grade thereof.
In the light of the above problems, it will be understood clearly that a conventional luster rating method and apparatus is not capable of properly indicating the clarity (image reflecting capability) of a surface.